The packing industry produces composite packaging materials having two or more, e.g. even fourteen layers for different applications, e.g. for packaging thermosetting fiber reinforced resins (pre-preg), food products and medicaments. From among these packaging materials with two-seven layers typically contain different polymer films wherein the aroma seal and the adhesion between the films are provided by a special oligomer film. These films are usually produced through the high-investment blown co-extrusion technology from polyamide (PA) and polyolefin films, characteristically from polypropylene (PP) films having a layer with excellent barrier property, such as ethylene vinyl alcohol (EVOH) film between them. Hereinafter these are called co-extruded films.
The waste management of the above waste packaging materials raises several problems. Their recycle may cause difficulties if they become contaminated with the residues of packaged materials, such as pre-preg. On the other hand, in co-extruded films the different polymer components are glued together. These components are usually hydrophilic polyamides and hydrophobic polyolefins, which are not compatible with each other and there is a 40-50° C. difference between their processing temperatures. Thus, the conventional compounding methods are not suitable for their homogenization, and their separation is not feasible even if the most advanced technologies are used.
A further problem is that the water absorption of polyamide can reach up to 3-5% by weight of polyamide and moisture should be removed during production otherwise polyamide will become unprocessable. However, water removal requires a lot of energy input. In view of the above, these film wastes are utilized primarily as inert filling materials.
Moreover, in Europe there is a widespread tendency to utilize them as energy materials, i.e. fuels, which is, however, in contradiction with the efforts to give preference to the reuse of waste materials in order to spare the Earth's resources. This is particularly true regarding materials produced by using high specific energy, such as co-extruded films.
One of the well-known methods of recycling polyamide/polyolefin film wastes is compounding them in a double-screw extruder, during which the wastes are melted, property-enhancing additives are introduced into them, then they are “kneaded” to obtain homogeneous material, after that the obtained material is granulated. Due to the high melting point of polyamide, this process should be performed at a temperature around 250° C., however the processing temperature of polyolefins is only 190° C. and at temperatures higher than this, polyolefins become highly degraded. Furthermore, any extra heat transfer step taken during the process leads to the partial degradation and property impairment of the polyolefins.
According to another process, polymers are separated on the basis of their density. Essentially, in this process a magneto-hydrostatic fluid is created and the phases with different fluid densities, formed in the process, are separated. By using this process, the polyolefins, polystryrene (PS), acrylonitrile butadiene syterene copolymers (ABS) and polyamide can be separated, however this process is not appropriate for separating the co-extruded film or an agglomerate containing it.
Hungarian Patent Application No. P0301987 (ExxonMobil Chemical Partners Inc.) describes thermoplastic polymer blends which contain only hydrophyl-hydrophyl end-groups, therefore, in their case the problem of homogenizing the hydrophylic-hydrophobic mixtures does not occur.
In Hungarian Patent No. 226 636 (Appl. No. P0500317) a vibration and noise reducing nano and micro composition of wide frequency range was produced from thermoplastic polymers by the recycle of tyre rubber powder. In this process the components were compatibilized by the use of ethylene vinyl acetate copolymer (EVAC).
European Patent No. EP1563007 (validated in Hungary under No. E001500) relates to products prepared from polymers not compatible with each other. According the disclosure, polymer tubes and inserts were produced by mixing melts of polyolefin, polyamide and a compatibilizing agent. Alkyl-carboxyl-substituted polyolefins were used as compatibilizing agent prepared by grafting carboxylic acids, anhydrides or esters to polyolefins.
The invention relates to the co-recycling of polyamide and polyolefin plastic wastes, such as film wastes or co-extruded film wastes, with fiber reinforced plastic or resin wastes. The aforementioned wastes are produced with high energy inputs, therefore, they imply high added value, furthermore, they possess excellent physical-mechanical properties, this is the reason why possibilities of their reuse were investigated.
The present inventor discovered that the addition of dicarboxylic acid anhydrides to the mixture of the above wastes can solve the problem of homogenizing the non compatible polyamide and polyolefin film wastes and the homogenization of co-extruded films containing polyamide and polyolefin layers, and additionally the incorporation of fiber containing wastes can be promoted. For the improvement of the properties of the product, further polymer materials can be added. These can also be waste materials, the recycling of which provides a solution to the management of further polymer wastes.
As a result of the present process a homogenous disperse polymer agglomerate is obtained, by the use of which as a base material, plastic products with excellent properties and with fiberglass-free surface are produced.